Canadian Forest Service Publications

Fire activity and severity in the western U.S. vary along proxy gradients representing fuel amount and fuel moisture. 2014. Parks, S.A.; Parisien, M.-A.; Miller, C.; Dobrowski, S.Z. PLoS ONE 9(6):e99699.

Year: 2014

Issued by: Northern Forestry Centre

Catalog ID: 35560

Language: English

CFS Availability: PDF (download)

Available from the Journal's Web site.
DOI: 10.1371/journal.pone.0099699

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Numerous theoretical and empirical studies have shown that wildfire activity (e.g., area burned) at regional to global scales may be limited at the extremes of environmental gradients such as productivity or moisture. Fire activity, however, represents only one component of the fire regime, and no studies to date have characterized fire severity along such gradients. Given the importance of fire severity in dictating ecological response to fire, this is a considerable knowledge gap. For the western US, we quantify relationships between climate and the fire regime by empirically describing both fire activity and severity along two climatic water balance gradients, actual evapotranspiration (AET) and water deficit (WD), that can be considered proxies for fuel amount and fuel moisture, respectively. We also concurrently summarize fire activity and severity among ecoregions, providing an empirically based description of the geographic distribution of fire regimes. Our results show that fire activity in the western US increases with fuel amount (represented by AET) but has a unimodal (i.e., humped) relationship with fuel moisture (represented by WD); fire severity increases with fuel amount and fuel moisture. The explicit links between fire regime components and physical environmental gradients suggest that multivariable statistical mod ls can be generated to produce an empirically based fire regime map for the western US. Such models will potentially enable researchers to anticipate climate-mediated changes in fire recurrence and its impacts based on gridded spatial data representing future climate scenarios.

Plain Language Summary

Canadian and US researchers looked at how fire severity is affected by the amount and moisture level of forests and plants that provide fuel for fires. While fire activity – the number of fires and area burned – has been studied extensively, severity – how drastically the fire changes the ecosystem and soils – has not been examined. The researchers studied remote sensing data for the western United States from 1984 to 2010 to measure the severity of fires. They estimated the amount of fuel in a given area from data on the moisture given off by plants (evapotranspiration), and the amount of moisture from “water deficit,” a measure of drought. They found that, although fires are more severe if there is more fuel, severity is low with both high- and low-moisture areas. High-moisture rainforests do not burn severely, but neither do very dry forests adapted to their climatic conditions. It is forests in moderate moisture conditions that are susceptible to severe fires during droughts. Overall, it found that fire severity is affected by the amount of fuel and its moisture. Understanding the effect of fuel on fire severity as well as activity helps predict the severity of fires and their effect on the ecosystem.